The exhaust valve of an internal combustion engine is exposed to hot corrosive exhaust gas at a temperature of more than about 800.degree. C. and, in the course of use, the valve neck is subjected to strong tensile and bending stresses in seating because of the tension of the valve spring and the inertia of the valve itself. At the same time, the exhaust valve is oxidized at the above-mentioned high temperature by CO.sub.2, H.sub.2 O or residual O.sub.2 in the exhaust gas and, in the case of a gasoline engine, it is also subjected to the hot corrosive action of the burned product of the lead compound which is added to the gasoline as an anti-knock agent. Moreover, impact wear takes place between the valve face and the valve seat during seating. These actions are aggravated in the case of an increased output or speed, so in designing an engine with high reliability and high speed, it is necessary to select a superior material for the exhaust valve.
At present the preferred material, both in Japan and abroad, for the internal combustion engine is 21-4N steel (Fe-0.5C-21Cr-4-Ni-9Mn-0.4N), but in view of the rigorous conditions under which the latest high performance engines operate, a valve steel having a greater high-temperature strength, resistance to oxidation and resistance to corrosion by lead oxide has to be developed. To meet this demand, there is an increasing tendency to build up an exhaust valve with stellite, but such a buildup operation is so complicated, requiring a number of steps, that it is economically disadvantageous; and particularly in the case of an engine subject to a heavy load the exhaust valve thus built up is unstable in performance.
Recently unleaded gasoline has come into use mainly in U.S. and Japan and regarding so called valve seat recession problem valve seat insertion is often resorted to as a remedy, but in that case the exhaust valve is exposed to a still higher temperature than before through valve seat insertion. Therefore it is necessary to increase still further the high-temperature strength and the resistance to hot corrosion of the exhaust valve. Furthermore, when a high-lead gasoline is used as has lately occurred abroad, an exhaust valve material having a still greater resistance to corrosion by lead oxide is necessitated.